ISSN: 2277-3754
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Lasergrammetry: New Approach for Monitoring
Structural Behavior of Vaults Dams Momayiz Kaltoum, Sounny Slitine Hafid, Anouar Abdellah
University Hassan Premier, FST Settat, Morocco Hydraulic Developments Direction, Rabat, Morocco
Abstract— For safety control and economic improvement,
the surveillance of the dams and their structural behavior
requires observation and monitoring with high accuracy. As
well, the stability of concrete vault dam depends on its overall
geometry, and the analysis results strongly rely on the
accuracy in which this geometry can be measured in practice.
And, with the progress of modern technology using the
Terrestrial Laser Scanners (TLS) in deformation
measurement, the accuracy is much improved. Currently, this
technology (TLS) is used in large and complex engineering
structures such as dams to better understand their behavior
due to its accuracy and speed in obtaining a cloud points 3D in
different time intervals. In fact, for the first time in Morocco,
the concrete vault dam named Asfalou, located in city of
Taounate, is used for case study in order to verify the
efficiency of the TLS results. This paper describes the main
steps of this approach and the assessment of its effectiveness
compared to the conventional method.
Index Terms—Vault dam, monitoring, TLS, point cloud
3D.
I. INTRODUCTION
The dams lead to economic and social benefits such as
irrigation, production of electrical energy, drinking water
supply, the fight against flooding and navigation along
the tank… They are also exceptional structures, not only
in their size, but perhaps above all by their duration [1]. It
results that the observation of dam behavior is a
requirement to ensure their safety. If monitoring of civil
engineering structures was first developed for the dams, it
is because more than others, these structures present risks
that it was imperative to control [2] and require
appropriate measures in the early stages to increase their
lifespan. Currently, damage and breakages of dams are in
increasing quantities due to ageing, earthquakes and
climate change. For these reasons, the dam safety has
gained more importance than ever in terms of disaster
management at the national. Considering the importance
of these structures, the International Commission of
Large Dams (ICOLD) has created in 1982 a technique for
monitoring which includes several activities: the design
of the monitoring plan, the installation of devices
monitoring, the reading of these devices at pre-
established frequency, the conversion of measures to
significant engineering quantities, the interpretation of
these quantities, the comparison with the models, the
visual inspection of the dam and the delivery of a safety
report. Monitoring activities are mainly related to
security, but also to collecting valuable data to improve
understanding of the behavior of these structures. During
the last decades, remote sensing technique or
lasergrammetry based on terrestrial laser scanner (TLS)
has improved [3] and become a complementary technique
to measure with high precision infrastructure
displacements [4] and without physical contact with the
object [5]. It should be noted that the operation of the
high data redundancy provided by TLS tools is a key to
getting good performance for measuring deformations
[6]. This study, based on the 3D point cloud, focuses on
vaults dams given the complexity and geometry of these
structures. The paper describes the main steps of the
procedure : the 3D survey by Leica C10 TLS, the point
clouds registration, the 3D drawing of cracks affecting the
downstream face of the vault, modeling and estimation of
different deformations. It also outlines the main
advantages of the proposed approach in comparison to the
traditional means for measuring surface deformation of
vaults dams, using as case Asfalou dam at the city of
Taounate.
II. PROBLEMATIQUE
It should be remembered that: preventive maintenance
improves the functioning of a dam, increases its lifespan
and significantly reduces risks to populations at the
downstream of the structure [7]; the stability of a masonry
arch dependent on its overall geometry; and analysis
results are highly dependent on the precision in which this
geometry can be measured in practice [8]. Monitoring is
carried by the operator of the dam. It takes two
complementary forms: first, visual surveillance leading to
regular inspection tours and the eye of an experienced
technician can be considered as one of the best available
sensors; secondly, auscultation of the dam with periodic
surveys by using measuring instruments [9].
The significant parameters of dam behavior usually
adopted are:
- Absolute or relative displacements
- Local deformations, possibly considered as
constraints
- Pore pressure or under-pressure
- Flow of drainage or leakage.
Thereafter, the development of measuring instruments
and operating and interpretation procedures results from
the need to answer to the designers and constructors
questions in order to understand the behavior of structures
and ensure their safety at any time of their existence[10].
With regard to the visual inspection, it looks at the
occurence of external pathologies that may affect the dam
face such as seepage and cracks. A crack that appears in a
gallery or in a place accessible to the dam team can be
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monitored by traditional means such as Vinchon system
or fissurometers [11]. In 1922, an important program of
instrumentation of arch dams was launched in the United
States. It aimed at the understanding of the mechanical
behavior of this type of dam in order to reduce costs and
increase their security. As part of this initiative,
fissurometers and inclinometers placed on the upstream
and downstream of the structures were used. In addition,
the internal deformations of concrete were measured by
using instruments constituted of sensors with variation in
resistance [12].
But for a large dam, detection of new cracks by visual
inspection can degrade the factor of fidelity to reality as
the agent identifies a number of cracks that might not
match the existing. In addition, until now the
representation of these cracks is done manually on a
sketch.
For the geodesic auscultation, it looks at studying the
movements of dams through conventional topographic
instruments by measuring the absolute displacements in a
surveillance network referenced to fixed points
materialized by benchmarks outside the area of influence
of dam.
In the last few years there has been an increasing
interest in exploiting the Terrestrial Laser Scanning (TLS)
data for deformation measurement and monitoring
purposes [13] with exceptional resolution and accuracy
[14]. The TLS became an instrument extensively used
both in architecture [15], civil engineering, [16]-[17]
archeology [18]-[19] and environmental studies [20]. It
allows quick acquisition of dense and textured 3D point
cloud with great precision and without direct contact with
the structure [21] .The acquired point cloud is attached to
the same reference coordinates system of the dam. Its
combination with geo-referenced images leads to the
creation of a real visualization model of the structure.
In the light of all these TLS features and in order to
take advantage of its efficiency and efficacy, an
experiment was carried out, the first in Morocco, on an
vault dam named Asfalou regard on its geometry and its
importance.
III. OBJECTIVES
The objectives of this study are:
Selecting stations surveying and 3D acquisition of
the downstream of the dam by TLS
Assessment of the accuracy and efficiency of TLS
performance for movement control and monitoring the
structural behavior of a dam.
Comparison between measurements and derived
products by TLS and those provided by conventional
means during the dam monitoring.
Creating a 3D database of the dam that can be
updated by the various surveys to ensure better
management of the structure.
Archiving the real time and real position witness, in
videos generated by the True View Application, which
can check the dam in case we doubt an external
pathologies that may affect the dam.
Standardization of a methodology for dam
surveillance by TLS from planning to results presentation
with maximum precision.
The development of a prevention action plan
according to the ageing evolution of the studied structure.
IV. EXPERIMENTATION
A. DAM DESCRIPTION
The chosen dam in this study is a vault dam named
Asfalou built in 1996 on the Asfalou River, located 65 km
from the city of Taounate Fig.1.
Fig 1 : ASFALOU dam, pecture taken from Hydraulic
Developments Direction of Morocco
B. SELECTION CRITERIA OF THE DAM
The choice of this dam is based on:
- Size: Presence of high hydrostatic pressure on the
upstream face of the dam given its important height,
112m.
- Design: thin vault dam
- The existence of a population downstream
- The flood control to enhance security at the dam
ALWAHDA
- Attenuation of siltation risk of the dam ALWAHDA
- Energy production: 30 million Kwh
- Contribution to the development of irrigation in the
basin Ouarga
- Adjustment of nearly 120Mm3 of water annually
mainly for the benefit of small and medium hydraulic
perimeters (PMH) located downstream.
In addition, some reasons related to the monitoring of
dam behavior including the occurrence of micro cracks
on the downstream face of the dam, whose appearance
dates remain not well known. It is a question to make a
3D survey of the downstream face of the Asfalou dam for
two thermally different periods: March and June 2012, to
analyze the different apparent deformations or
displacements and to compare with the results provided
by the traditional means of auscultation.
IV. MATERIELS AND METHODS
USED MATERIELS
The inspection of a dam by TLS requires two phases:
ISSN: 2277-3754
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1. Field phase
Scanning the downstream face of the Asfalou dam was
conducted by a laser scanner C10 with a resolution <1mm
over a range of 300m to which is integrated a camera of
very high definition and large focal length Table1. The
field survey required 6 hours for the survey of the dam
downstream side without any contact by creating a
topographic polygonal attached to the system of the dam
Fig. 2.
Fig 2: Image obtained from 3D point cloud
2. Office Phase
To process the 3D point cloud, several software are
combined such as Cyclone, Cloud works, Cyclone topo2
and 3DRechaper. They are used for restitution and
mapping of different cracks and pathologies affecting the
downstream face of the dam during different times of the
survey in the same coordinates system of the dam Fig.3.
Fig. 3: Real mapping of cracks
They also allow 3D modeling and inspection of dam
deformation Fig.4 with the possibility to export files to
CAD software such as AutoCAD for overlay and
comparison Fig.5.
Fig 4: from top to bottom : Modeling and inspection of
deformations
Fig 5: Mapping cracks and their overlay on Autocad
V. RESULTS AND ANALYSIS
A. RESULTS PROVIDED BY TRADITIONAL
AUSCULTATION MEANS
Currently, the monitoring of Asfalou dam behavior is
achieved by a number of conventional instruments such
as: direct Pendulum, inverted pendulum, extensometer,
Vinchon, glass lamp on the cracks and scale staff gauge
for measuring the level in the reservoir.
To monitor the development of cracks, glass witnesses
or paint Fig.6 are used to identify them. They are
numbered in a sketch Fig.8. This method is effective for
the quick detection of any development because the glass
witnesses breaks at the opening of the crack, provided
that it is well stuck because if not the crack can develop
without being detected. Whereas for monitoring of the
behavior of the joints between the sections of the face of
the dam, a Vinchon system is installed on each joint, and
measures are regularly taken by the dam agents Fig.7.
Fig 6: from left to right: glass witnesses or paint
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Fig 7: Vinchon on joint
The results of all these methods are shown in manual
sketches which unfortunately remain a schematic
representation of cracks Fig.8, of seeps localization Fig.9
and do not cover the entire surface of the downstream
face of the dam because there are cracks inaccessible
given the height of the dam.
In addition, the measures provided by direct and
inverted pendulums to get the direction of the dam
displacement and the temperature probe in the same dates
of the TLS survey (March-June 2012) are summarized in
the table 2.
Fig 8: Sketches of cracks, from Hydraulic Developments
Direction of Morocco
Fig 9: Sketches of seeps, from Hydraulic Developments
Direction of Morocco
B. ANALYSIS OF RESULTS PROVIDED BY
AUSCULTATION TRADITIONAL MEANS
From table 2, it can be noticed that the measures taken
by the direct pendulum showed variation of 2.97mm from
downstream to upstream and of 0.29mm bank-bank. This
implies that the high point of the direct pendulum has
shifted to upstream from the low point of 2.97mm. The
same to the inverted pendulum, the measures showed a
displacement of 0.42mm, which shows that the vault has
moved 0.42mm from downstream to upstream. Therefore,
the downstream face of the dam has tends to expand more
than the upstream face and the vault will lean upstream.
This can be also confirmed by the thermal effect which
has increased from March to June.
C. RESULTS PROVIDED BY TLS
In addition to the mapping and 3D localization in the
dam coordinates system of all cracks and seeps present
on the downstream face Fig.10, the point cloud provided
by the C10 laser scanner allows modeling and inspection
of the different deformations along the face and offers a
real photographic coverage and a rich archive of 3D real
videos of all that is visible in the field of view of the TLS.
Zoom
Zoom
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Fig 10: from top to bottom : defects of drains, seeps and
images of cracks.
D. ANALYSIS OF RESULTS PROVIDED BY TLS
The analysis of the results provided by TLS shows that
cracks have undergone extensions during the period from
March to June table 3. This explains that the downstream
face of the dam has expanded more than the upstream
face between the two survey periods. Also, the inspection
of deformations provided by 3DReshaper Fig. 4 and the
overlay of mapped cracks in both periods Fig. 5 show that
the dam has moved a few millimeters in the directions
upstream-downstream and bank-bank. This joined the
same interpretation of Table 1 and clearly confirms the
results obtained by conventional means.
VI. CONCLUSION
The rapid acquisition of 3D information with very high
density is among the strengths of the Lasergammetry in
monitoring dams. Scanning by TLS is the most
appropriate way to acquire various pathologies affecting a
dam in a record time. It offers a dense 3D point cloud,
can scan dangerous and inaccessible parts whose distance
from the face of the dam can reach tens or even hundreds
of meters. Results representation is also considered
among the benefits of this technology in the inspection of
cracks and deformations: compared to a manual sketch,
DXF or DWG plan of cracks is more advantageous that
the control and monitoring of the cracks evolution is
automated and more accurate. Also, the combined use of
laser scanning and digital imaging allows the generation
of textured model of the scanned part of the dam. The
fusion of these two data types is a valuable advantage for
semantic interpretation of several significant phenomena
for dam safety: it enhances the visual inspection by giving
clearer information on pathologies including their precise
location. Likewise, a 3D video, accurate in time and
position, allows performing measurements and adding
comments. With this type of model, the production of
new documents for the visual inspection of the dam will
improve the ability to assess in less time and more
precisely the history or the status of a dam. Thus, we
recommend benefiting of the advantages of TLS and of
Geographic Information Systems (GIS) to develop a GIS
application for automating the dam inspection.
Table 1: Technical characteristics of the TLS C10,
www.leica-geosystems.com/hds
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Table2: Measured parameters of the dam Asfalou taken from Hydraulic Developments Direction of Morocco
Legend:
AA: Displacement measure by pendulum from upstream to downstream
RR: bank-bank displacement measure by pendulum
Table 3: Cracks evolution
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Date of
mesure in
2012
Direct pendulum
(mm)
Inverted pendu-
lum (mm)
Temperature probe (°)
(TS)
AA RR AA RR TS1 TS2 TS3 TS4 TS5 TS6
March 9.26 2.26 -2.47 -0.13 14.30 14.39 13.92 12.62 15.67 12.55
Iune 12.23 2.55 -2.05 -0.18 13.57 14.24 16.11 12.66 16.63 15.49
Crack number Length in March (m) Length in June (m) Difference (mm)
Crack 1 7,3157 7,3169 1,2
Crack 2 3,1378 3,1383 0,5
Crack 3 3,0498 3,0498 0,0
Crack 4 1,0032 1,0085 5,3
Crack 5 1,8270 1,8333 6,3
Crack 6 0,5980 0,6006 2,6
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PLICATION TO THE RANGITIKEI CANYON (N-Z),‖
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AUTHOR’S PROFILE
MOMAYIZ Kaltoum, presently she is
a PhD Student and directress of the
company Globétudes of topography
studies and engineering.
Education
- 1996: the State Engineer degree in
topography at the Agro nomic and
Veterinary Institute HASSAN 2 (IAV HASSAN2), Rabat, Morocco;
- 2012: Obtaining the Master in Civil Engineering at Faculty of
Science and Techniques, Hassan 1st University, Settat, Morocco;
- 2012-2015: PhD Student.
Academic guidance and teaching
- 2006-2008: Supervision of engineers in machinery at IAV hassan2;
- 2008-2015: Referee and examiner several theses at IAV hassan2;
- 2012-2015: Supervision of Masters in Civil Engineering, agricultural
engineering and management and quality to the FST SETTAT.
SOUNNY SLITINE Hafid, Engineer dams in the Hydraulic Devel-
opments Direction, graduated from the Mohammedia School of Engi-
neering in 1995.
Education
- 1995: State Engineer in Civil Engineering, Option Buildings,
Roads and Bridges at Mohammedia School of Engineering, Ra-
bat,Morocco;
- 2003-2004: Masters in Télélédétection and Geographic Informa-
tion Systems – CRASTE.
Professional Experience and Academic guidance
- Responsible for auscultation of 12 major dams at Hydraulic
Developments Direction, Morocco;
- Establishment of auscultation projects of dams and monitoring
their implementation (Choosing the auscultation device and es-
tablishment of site plans);
- Realization of a study of siltation project Taifine basin by re-
sources of GIS and Remote Sensing;
- Realization of an application of auscultation report manage-
ment;
- Contribution to feedback between dams in operation and ex-
ecution dams;
Supervision of studies ends of project engineering students.
ANOUAR Abdellah, the head of the chemistry department of Ap-
plied and Environmental also Professor of Higher Education in the
Faculty of Science and Techniques Settat, Hassan 1st University, Mo-
rocco.
Education
- 1989: Degree in Chemistry;
- 1992: Ph.D in France;
- 2001: Ph.D in Morocco.
Publication
He published 8 researches in 2014 primarily in Water Treatment, be-
low some of his publications:
- Belbahloul Mounir, Anouar Abdellah and Zouhri Abdeljalil.
Low Technology Water Treatment: Investigation of the Perfor-
mance of Cactus Extracts as a Natural Flocculant for Floccula-
tion of Local Clay Suspensions. International Journal of Engi-
neering Research & Technology. Vol. 3 Issue 3, March – 2014;
- Asmaa Karboubi, Abdeljalil Zouhri, Abdellah Anouar²
Characterization of Domestic Waste water and Performance In-
dicators of the Waste water Treatment Plant of the City of Set-
tat.International Journal of Engineering Research & Technology,
Vol. 3 - Issue 2 , February – 2014;
- Aziz Akhiate, Al alami Semma, Abdelah Anouar, « Austenitic
grain size quantification of martensitic low carbon stainless
steel», IOSR Journal of Mechanical and Civil Engineering
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(IOSR-JMCE) e-ISSN: 2278-1684,p-ISSN: 2320-334X, Volume
11, Issue 5 Ver. VI (Sep- Oct. 2014), PP 50-56.